1. Field of the Invention
This invention relates generally to a Radio Frequency Identification (RFID) transponder and, more specifically, to a high gain low current input stage for an RFID transponder.
2. Description of the Prior Art
It is desirable to have a sensitive input into a transponder. In order to do this, one must amplify the input signal. Presently, most input stages require the use of a decoupling capacitor. The decoupling capacitor is required to isolate the DC bias component generated by the amplifying circuit from the external L-C circuit. It is desirable to isolate the DC bias component since one does not want the DC component to be short-circuited to ground via the inductor element of the external L-C circuit. Furthermore, the problem with using a decoupling capacitor is that the decoupling capacitor that is required is very large and consumes valuable silicon real estate.
Therefore, a need existed to provide an improved high gain input stage for a transponder. The improved high gain input stage must require fewer components to implement than prior art input stages. The improved high gain input stage must not require a decoupling capacitor. The improved high gain input stage must allow an automatic gain control circuit to be easily integrated therein. The improved high gain input stage must further have a low current consumption.
In accordance with one embodiment of the present invention, it is an object of this invention to provide an improved high gain input stage for a transponder.
It is another object of the present invention to provide an improved high gain input stage for a transponder which requires fewer components than prior art input stages.
It is still another object of the present invention to provide an improved high gain input stage biasing circuit for a transponder that does not require a decoupling capacitor.
It is yet another object of the present invention to provide an improved high gain input stage for a transponder wherein an automatic gain control circuit may be easily integrated therein.
It is still a further object of the present invention to provide an improved high gain input stage for a transponder that has a low current consumption.
In accordance with one embodiment of the present invention, a high gain input stage for a Radio Frequency Identification (RFID) transponder is disclosed. The high gain input stage uses an amplifier for increasing a magnitude of an input signal. A DC bias circuit is used for controlling the operation of the amplifier. A resonant circuit is coupled between the amplifier and the DC bias circuit. The resonant circuit is used for receiving a signal generated by an electromagnetic field and for generating the input signal which is sent to the amplifier. The resonant circuit has an inductive portion which is used to DC bias the amplifier.
In accordance with another embodiment of the present invention, a method of providing a high gain input stage for a Radio Frequency Identification (RFID) transponder is disclosed. The method comprises the steps of: providing an amplifier for increasing a magnitude of an input signal; providing a DC bias circuit for controlling operation of the amplifier; and providing a resonant circuit coupled between the amplifier and the DC bias circuit for receiving a signal generated by an electromagnetic field and for generating the input signal sent to the amplifier wherein an inductive portion of the resonant circuit is used to DC bias the amplifier.
The foregoing and other objects, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiments of the invention, as illustrated in the accompanying drawings.